In the fields of biotechnology and nanotechnology, it is often useful to precisely dispense very small desired quantities of fluids in some desired pattern on a substrate. As an example, in the field of nanotechnology, it can be useful to situate lines or other patterns of catalysts or nucleation agents on a substrate to ready it for the later growth or deposition of other materials at these sites. As another example, in the field of biotechnology, it is often useful to situate arrays of “spots” of oligonucleotides on glass slides or other substrates for use in the later analysis of nucleic acid sequences. At the time this document was prepared, some microarray spotters are able to accomplish spot sizes on the order of 75 micrometers using dispensation methods such as the use of quill pens. However, quill pen dispensation suffers from the disadvantage that over time, as quill tips (which can cost as much as several hundred dollars per tip) degrade, spot sizes grow and become more irregular. Additionally, while the ability to generate spots having diameters on the order of 75 micrometers is useful for applications such as generation of biological microarrays, the ability to generate still smaller spot sizes would be valuable.
Other exemplary apparata for dispensation of microvolumes of fluids are described in U.S. Pat. Nos. 6,220,075, 6,112,605, 6,083,762, 6,079,283, and 5,927,547 to Papen et al.; U.S. Pat. Nos. 5,658,802 and 4,877,745 to Hayes et al.; U.S. Pat. No. 6,232,129 to Wiktor; and U.S. Pat. No. 6,296,811 to Sasaki. As these patents illustrate, a common arrangement used for fluid microvolume dispensation is to provide an elongated nozzle (e.g., a pipette or other tube) which has a piezoelectric tube or ring element surrounding at least a portion of its length. The piezoelectric tube/ring is situated between the dispensing end of the nozzle (the end from which fluid is to be dispensed), and an opposing end which is usually attached to a fluid supply via rigid or flexible tubing. The dispensing end of the nozzle is situated slightly above the substrate upon which fluid is to be deposited. The piezoelectric tube/ring is then powered at frequencies generally ranging in the sonic (less than 20 kHz) or ultrasonic ranges, and at amplitudes ranging from 20-150V; see, e.g., U.S. Pat. No. 6,232,129 at column 5 lines 28-35, and/or U.S. Pat. No. 6,296,811 at column 5 lines 23-33. The piezoelectric tube/ring then expands and contracts at this excitation frequency, resulting in corresponding expansion and contraction of the interior of the piezoelectric tube/ring, and thus the adjacent nozzle walls which the tube/ring surrounds. Fluid resting within the nozzle is then expelled from the nozzle's dispensing end by what appears to be an action similar to peristaltic pumping, with the opposite end of the nozzle being supplied with further fluid from the fluid supply. By use of this arrangement, dispensation of microvolumes as small as 10 picoliters (0.01 nanoliters) is reported (see, e.g., U.S. Pat. No. 6,296,811 at column 5 line 51 onward). This corresponds to spot sizes as small as approximately 35 micrometers in diameter, assuming an aqueous solution is deposited on a glass slide (which is moderately hydrophilic).
Arrangements of this nature can also be used for fluid aspiration (fluid removal) rather than fluid dispensing. U.S. Pat. No. 6,232,129 notes (at column 5 line 56-column 6) that a nozzle can be used to aspirate fluid from a fluid supply by inserting an empty nozzle's dispensing end within a fluid supply and actuating the piezoelectric tube/ring. It appears that when the piezoelectric ring/tube is vibrated, any fluid flows in the nozzle in the direction of least resistance/lower pressure (i.e., from within the fluid collected within the nozzle to the atmosphere when dispensing, or from the fluid supply to the empty interior of the nozzle when aspirating).
An apparently different form of vibrational aspiration is described in U.S. patent application Ser. No. 09/617,478 (now U.S. Pat. No. 6,638,249), naming inventors Amit Lal and Chung-Hoon Lee and assigned to the assignee of the present invention. This document describes improved hypodermic-type needles wherein an outer needle having a sharpened end may be inserted within a body, and an inner tube situated within the outer needle may be ultrasonically vibrated to aspirate fluid from the outer needle (and thereby cause the outer needle to aspirate fluid from the body). The inner tube rests atop a silicon horn which is in turn coupled to an ultrasonic actuator driven at 100 kHz-1 megahertz or higher. The horn is connected to a frame which bears the outer needle in a manner such that transmission of vibrations to the outer needle is minimized. The arrangement is somewhat bulky owing to the need to mount the inner needle within the outer needle in such a manner that vibrational coupling between the two is minimized.
A disadvantage of the prior piezoelectric ring/tube nozzles is their size, complexity, and cost. Cost and complexity are issues owing to the need to manufacture a piezoelectric tube/ring wherein a nozzle can be inserted with close coupling between the structures. Size is problematic since it will often be useful to provide multiple adjacent nozzles which dispense onto the same substrate (each often depositing a different fluid), thereby allowing rapid dispensation of multiple spots or other features. However, looking to nozzle arrangements such as those shown in FIG. 1 of U.S. Pat. No. 6,232,129, and FIG. 2 of U.S. Pat. No. 6,001,309, there are apparent difficulties in providing such nozzles sufficiently closely spaced in an array that they can be simultaneously used to dispense fluids on the same small substrate (e.g., on the same microarray slide). Additional difficulties would be encountered with nozzle arrays because the size of deposited spots may vary in accordance with the distance of the dispensing end of each nozzle from the substrate, and if the heights of the various nozzles are not precisely aligned so that their dispensing ends are spaced at the same distance from the substrate's surface, the spot sizes produced by the various nozzles will vary. It might instead be possible to use only a single nozzle to sequentially deposit different fluids on a substrate, with the nozzle being interchanged between fluids (and rinsed between changes), but this approach leads to a significant increase in process time and can also result in unnecessary waste where the fluid being deposited is scarce.
The piezoelectric ring/tube arrangement also has the disadvantage that fluid dispensation/aspiration will not be effective unless the nozzle is “primed” with fluid to such a height that the fluid rests at or near the level of the piezoelectric ring/tube, else the expansion and contraction of the piezoelectric ring will not successfully enable pumping (see, e.g., U.S. Pat. No. 6,232,129 at column 5 line 36 onward). This implies that the foregoing arrangements may be unsuitable for use in microdispensation of fluids which are only available in extremely limited quantities, since the nozzle may need to be supplied with more fluid than is intended for dispensation owing to the need to prime the nozzle.